(A) Field of the Invention
The present invention is related to a manufacturing method for an electrode apparatus of a battery, more specifically, to a manufacturing method for an electrode apparatus of a battery capable of over-current protection, with a view to increasing resistance stability thereof.
(B) Description of Related Art
For the present broad application of portable electronic products, such as mobile phone, notebook computer, digital camera, personal digital assistant (PDA), etc., the use of over-current protection devices to prevent short circuit caused by an over-current or over-heating effect in a secondary battery or circuit device is becoming more and more important.
Conventionally, a positive electrode is essentially constituted of an upper electrode plate, an over-current protection device and a lower electrode plate, where the over-current protection device is sandwiched between the upper and lower electrode plates. The over-current protection device is a lamination constituted of an upper metal foil, a current-sensitive layer and a lower metal foil, where the upper and lower metal foils may be formed by electroplating copper onto nickel alloy.
The current sensitive layer may be composed of positive temperature coefficient (PTC) conductive material including polymer and a conductive fillers. Because PTC conductive material is sensitive to temperature variation, it can be kept extremely low resistance at normal operation because of its low sensitivity to temperature variation so that the circuit can operate normally. However, if an over-current or an over-temperature event occurs, the resistance will immediately increase to a high resistance state (e.g., above 104 ohm.) Therefore, the over-current will be reversely eliminated and the objective to protect the circuit device can be achieved.
In the air, the upper and lower metal foils made of pure nickel or of nickel alloy electroplated with copper most likely form films of oxidized copper or oxidized nickel on the surfaces. The oxidation films, normally very thin, are formed unexpectedly in accordance with the manufacturing process, inducing the thicknesses of the oxidation films to be non-uniform so that the resistance of the positive electrode is affected. Accordingly, various resistances of electrode apparatuses may be found in mass production, which would negatively affect quality control.